The present invention relates to an internal combustion engine. The invention is applicable on vehicles, in particularly heavy vehicles, such as e.g. trucks. However, although the invention will mainly be described in relation to a truck, the internal combustion engine is of course also applicable for other type of vehicles, such as cars, industrial construction machines, wheel loaders, etc.
For many years, the demands on internal combustion engines have been steadily increasing and engines are continuously developed to meet the various demands from the market. Reduction of exhaust gases, increasing engine efficiency, i.e. reduced fuel consumption, and lower noise level from the engines are some of the criteria that becomes an important aspect when choosing vehicle engine.
Furthermore, in the field of trucks, there are applicable law directives that have e.g. determined the maximum amount of exhaust gas pollution allowable. Still further, a reduction of the overall cost of the vehicle is important and since the engine constitutes a relatively large portion of the total costs, it is natural that also the costs of engine components are reduced.
In order to meet the described demands, various engine concepts have been developed throughout the years where conventional power cylinders have been combined with e.g. a pre-compression stage and/or an expansion stage.
U.S. Pat. No. 967,828 disclose an internal combustion engine with an object of minimizing the number of cylinders and moving parts required to perform an engine cycle. The internal combustion engine in U.S. Pat. No. 967,828 comprises a high-pressure cylinder and a low-pressure cylinder, which are connected to each other by means of two conduits. The low-pressure cylinder is equipped to alternately perform the functions of a compressor and an expander. Hereby, the need of a separate compressor and a separate expander is reduced.
Although the internal combustion engine disclosed in U.S. Pat. No. 967,828 provides a relatively compact engine with less components in comparison to its prior art engines, it is still in need of further improvements in terms of e.g. power efficiency.
It is desirable to provide an internal combustion engine having increased power efficiency in relation to prior art engines.
According to a first aspect of the present invention there is provided an internal combustion engine comprising a first low-pressure cylinder housing a first low-pressure piston; and a first high-pressure cylinder housing a first high-pressure piston, the first high-pressure cylinder being arranged in upstream fluid communication with the first low-pressure cylinder for providing exhaust gas into the first low-pressure cylinder; wherein the internal combustion engine further comprises a second low-pressure cylinder housing a second low-pressure piston, the second low-pressure cylinder being arranged in upstream fluid communication with the first high-pressure cylinder for providing compressed gas into the first high-pressure cylinder; and a second high-pressure cylinder housing a second high-pressure piston, the second high-pressure cylinder being arranged in downstream fluid communication with the first low-pressure cylinder for receiving compressed gas from the first low-pressure cylinder, and further arranged in upstream fluid communication with the second low-pressure cylinder for providing exhaust gas into the second low-pressure cylinder.
The high-pressure cylinder is, according to an example embodiment, a combustion cylinder. The combustion cylinders may in an example embodiment, as will be described further below, be four-stroke combustion cylinders, i.e. they have one power stroke and one exhaust stroke for every two revolution of the second crank shaft. When the high-pressure piston in the respective combustion cylinders are travelling downwards, towards a bottom dead centre of the respective cylinder, compressed gas from the low-pressure cylinder is forced into the combustion cylinder. When the high-pressure piston thereafter is travelling upwards toward a top dead centre of the combustion cylinder, the gases in the combustion cylinder are compressed and ignited at a desired point in time. The high-pressure piston is thereafter, again, traveling downwards towards the bottom dead centre. Finally, when the high-pressure piston is travelling upwards, the exhaust gases are directed out from the combustion cylinders and in to the other one of the low-pressure cylinders. Combustion fuel is provided to the combustion cylinders in a fashion known to the person skilled in the art of four-stroke internal combustion engines and will not be discussed further. The invention is also not limited to any particular kind of fuel.
The low-pressure cylinders according to the present invention each has the dual functioning of operating both as a compression cylinder as well as an expansion cylinder.
A compression cylinder should in the following and throughout the entire description be interpreted as a cylinder which is arranged to provide compressed gases into the high-pressure cylinders. Accordingly, the low-pressure piston compresses gas inside the low-pressure cylinder, which compressed gas thereafter is provided to the intake of one of the high-pressure cylinders. The pressure level of the compressed gas is then above atmospheric pressure.
An expansion cylinder should in the following and throughout the entire description be interpreted as a cylinder which is arranged to receive exhaust gas from the high-pressure cylinder and thereafter further provide the exhaust gas out from the expansion cylinder.
Hereby, the first low-pressure cylinder is arranged to provide compressed gas which is directed to the second high-pressure cylinder. The second high-pressure cylinder executes a combustion cycle and directs exhaust gases into the second low-pressure cylinder where the exhaust gases are expanded. Likewise, the second low-pressure cylinder is arranged to provide compressed gas which is directed to the first high-pressure cylinder. The first high-pressure cylinder executes a combustion cycle and directs the exhaust gases into the first low-pressure cylinder where the exhaust gases are expanded. The exhaust gases may, after being expanded in the first and second low-pressure cylinder, be directed to e.g. some sort of gas after treatment system, such as a catalyst or the like.
Accordingly, the first low-pressure cylinder is acting as a compression cylinder when providing compressed gas into the second high-pressure cylinder, and acting as an expansion cylinder when receiving exhaust gas from the first high-pressure cylinder. Likewise, the second low-pressure cylinder is acting as a compression cylinder when providing compressed gas into the first high-pressure cylinder, and acting as an expansion cylinder when receiving exhaust gas from the second high-pressure cylinder.
Furthermore, the wording “fluid communication” should not be construed as limited to a specific fluid, or state of a fluid. The fluid may for example be in a gas-phase, or a liquid-phase.
The present invention is based on the insight that by arranging a low-pressure cylinder to function as a compression cylinder for one of the high-pressure cylinders, and as an expansion cylinder for the other one of the high-pressure cylinders, a compact cylinder arrangement is provided in which a reduction of dead volume in the low-pressure cylinders can be provided since the low-pressure cylinders will receive exhaust gases which are already pressurized from a compression stage.
Furthermore, another advantage of the present invention is that the low-pressure cylinders can function as compression cylinders as well as expansion cylinders without the need of a dual-acting piston, since both the compression and the expansion takes place in the volume which is delimited by the cylinder liner and the upper portion of the piston reciprocating within the cylinder.
According to an example embodiment, the first and second low-pressure pistons may operate in a two-stroke configuration and the first and second high-pressure pistons may operate in a four-stroke configuration. According to an example embodiment, the first and second low-pressure pistons may be connected to a first crank shaft and the first and second high-pressure pistons may be connected to a second crank shaft, wherein the second crank shaft is configured to rotate with a speed of at least twice the speed of the first crank shaft.
Hereby, when the second crank shaft rotates with a speed twice the speed of the first crank shaft, the four-stroke high-pressure pistons completes a full combustion cycle, which is 720 crank angle degrees, when the low-pressure pistons completes a full two-stroke cycle, which is 360 crank angle degrees. To transfer the torque from the first crank shaft and the second crank shaft to e.g. the gearbox transmission, and to synchronize the crank shafts, the first crank shaft may be connected to the second crank shaft by means of e.g. a suitable transmission. It should be readily understood that the wording “at least twice the speed” should be interpreted in such a way that the second crank shaft should rotate with a speed having a multiple integer of at least two.
According to an example embodiment, the first low-pressure piston and the second low-pressure piston may be arranged in a 180 degrees crank angle offset in relation to each other, such that the first low-pressure piston is configured to reach an upper end position within the first low-pressure cylinder when second low-pressure piston reaches a lower end position within the second low-pressure cylinder. Hereby, a continuous torque is provided. Also, the combustion process and expansion process will be relatively continuous which will result in an optimized combustion cycle.
According to an example embodiment, the first high-pressure piston and the second high-pressure piston may be positioned to reach an upper end position within the respective high-pressure cylinder approximately simultaneously and in such a way that the first high-pressure piston is configured to be ignited at an upper end position within the first high-pressure cylinder when the second high-pressure piston is in an upper end position within the second high-pressure cylinder for initiation of intake of fuel therein. Hereby, a well-balanced engine is provided which has a continuous engine torque.
According to an example embodiment, the first and second high-pressure pistons may be arranged to reach a lower end position within the respective first and second high-pressure cylinder when the first and second low-pressure pistons reaches an upper and a lower end position within the respective first and second low-pressure cylinder.
According to an example embodiment, the first and second low-pressure cylinders may be provided with liner intake ports at a lower end portion of the respective cylinders, such that gas can be provided into the respective low-pressure cylinder when the respective first and second low-pressure piston is positioned in their lower end position.
Hereby, at the beginning of the compression phase, gas is provided into the low-pressure cylinder when the low-pressure piston is positioned in a lower end position therein, i.e. at a bottom dead centre of the low-pressure cylinder. At this stage, the low-pressure piston receives “fresh” gas, e.g. ambient air, into the low-pressure cylinder via the liner intake ports, and at the same time, or approximately the same time, expanded combustion gases are evacuated from the low-pressure cylinder. Hereby, a scavenging effect of the cylinder is provided.
The present invention is however not limited to liner intake ports at the lower end position of the cylinder, the invention works equally as well with ports located in e.g. the cylinder head of the low-pressure cylinder, such that “fresh” gas is received from an upper portion of the cylinders instead of the lower portion.
According to an example embodiment, the first low-pressure cylinder may be in fluid communication with the second high-pressure cylinder by means of a first passageway. According to an example embodiment, the second low-pressure cylinder may be in fluid communication with the first high-pressure cylinder by means of a second passageway. According to an example embodiment, each one of the first and second passageways may be provided with cooling means for cooling the fluid passing there through. By means of the cooling means, the power consumption of e.g. the compression cylinder can be reduced, since the pressure level of the cooling means can be increased in comparison to previously known engines.
Further, the total compression work will be reduced. A colder internal combustion engine is also provided. The cooling means may e.g. be a heat exchanger or the like. Still further, in a conventional two-stroke combustion engine, the temperature of the residual gases from the combustion process is relative high which results in additional compression work and increased energy losses in terms of increased cooling losses. However, with the cooling means of the present invention, the residual gases from the scavenging process in the low-pressure cylinder are cooled before entering the combustion cylinder thus solving the problem arising in conventional engines.
According to an example embodiment, the first high-pressure cylinder may be in fluid communication with the first low-pressure cylinder by means of a third passageway. According to an example embodiment, the second high-pressure cylinder may be in fluid communication with the second low-pressure cylinder by means of a fourth passageway.
According to an example embodiment, each of the high-pressure cylinders may comprise valved inlet ports and valved outlet ports for controlling fluid transportation into and out from the respective high-pressure cylinders. According to an example embodiment, each of the low-pressure cylinders may comprise valved outlet ports arranged to control fluid transportation out from the respective low-pressure cylinders.
It should be noted that the low-pressure cylinders may not need valved inlet ports, or the like, at the passage where combustion gases are provided from the respective high-pressure cylinders. Hence, the low-pressure cylinders may, according to the example embodiment, comprise valved outlet ports for the passage to the high-pressure cylinders as well as to the surrounding where the low-pressure cylinders discharges the expanded exhaust gases.
Due to the different speed of the crank shafts for the different cylinders, one common cam shaft may be sufficient to use, since the cam shaft for a two-stroke cylinder should run at the speed of the two-stroke crank shaft and the cam shaft for the four-stroke cylinders should run with a speed of half the speed of the four-stroke crank shaft. Hereby, due to the speed ratio between the first and second crank shafts described above, one common cam shaft may be enough to use. However, the present invention should not be construed as limited to only one cam shaft, the invention also functions properly by utilizing more than one cam, shaft, such as two or three cam shafts, etc.
According to a second aspect of the present invention, there is provided a vehicle comprising an internal combustion engine according to any one of the above described example embodiments.
Effects and features of this second aspect are largely analogous to those describe above in relation to the first aspect of the present invention.
Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.